1. Field of the Invention
The invention relates to servicing of refrigeration systems and more particularly to a system and method for automatically cleaning, testing and charging a refrigeration system used for cooling of an automobile passenger compartment.
2. Description of the Prior Art
Most refrigeration systems used for air cooling employ one of a class of substances known as refrigerants as a working fluid. A refrigerant is used to transport heat. The temperature of any compressible fluid rises with compression and falls with decompression. Refrigeration systems (or any heat pump) use cycles of alternating compression and decompression of their working fluid, occurring at mutually spaced locations, to transport heat from one location to another. Where compression of the working fluid raises its temperature above the ambient temperature, heat can be passed from the fluid to the environment. The quick loss of heat is facilitated by the passing the compressed working fluid through a heat exchanger. As compression of the working fluid is lost, the fluid falls in temperature. When the temperature falls below that of the environment, the working fluid can be passed through a second heat exchanger allowing it to absorb heat from the environment. By moving the working fluid between the two heat exchangers the system transports heat from the second heat exchanger to the first heat exchanger. By sealing the environments in which the heat exchangers are located off from one another, the environment housing the second heat exchanger can be cooled.
Refrigerants are those compressible fluids which are particularly efficient at transporting heat. Where used for maintaining a comfortable "room temperature", they should be good at transporting heat in a range around room temperature. They should remain in a compressible state well below the freezing point of water. Atmospheric air does not make for a particularly efficient refrigerant. Water vapor makes such a poor refrigerant as to be considered a serious contaminant if found in the working fluid of a refrigeration system.
Refrigeration systems are sealed against the incursion of air and water vapor, and against the loss of refrigerant, to prevent reduction in the efficiency of the system. However, refrigeration systems can leak, losing working fluid to the atmosphere, and gaining contaminants from the atmosphere. Therefore the compression/decompression cycle of refrigeration systems must occasionally be opened to allow replacement of the working fluid.
Replacement of the refrigerant in a refrigeration system requires replacement both of the refrigerant and a system lubricant. The greater the purity of the new refrigerant and lubricant is kept, the better. During servicing, purity is achieved by as complete as possible a cleaning of the refrigeration system before introduction of the new refrigerant and lubricant. After initial discharge of the old material from the refrigeration system, nearly complete cleaning is achieved by putting the refrigeration system under a vacuum. Liquid residue, particularly water, is vaporized under vacuum and withdrawn by a vacuum pump. Thereafter, pressurized refrigerant and lubricant are forced into the evacuated refrigeration system.
U.S. Pat. No. 4,688,388 to Lower et al. describes a automated system for charging a refrigeration system. As described in the '388 patent, a microprocessor based controller controls the sequence and duration of the application of vacuum and the introduction of oil and refrigerant to a refrigeration system. Solenoid actuated valves are used to selectively connect a vacuum pump and reservoirs of refrigerant and lubricating oil, to the compression/decompression cycle. Duration of the vacuum is timed. The period of connection of the lubricant and refrigerant reservoirs is determined by changes in weight of the contents of the reservoirs, as measured by a scale on which the reservoirs rest.
Programming of the charging apparatus taught in the '388 patent by an operator is aided by provision of a numeric keypad and other control keys, through which selection of, a given mode of operation, e.g. vacuum mode, may be made, duration of the vacuum mode may be made, or quantity of refrigerant may be made. Information relating to charging system status and error conditions are provided on an output display.
However, the '388 patent does not teach incorporation of tests useful in detecting fault conditions of the refrigeration system. Such faults may have contributed to contamination of the old working fluid. The '388 patent also fails to monitor conditions within the recharging system which compromise or prevent carrying out a recharging operation.